A cell, or secondary battery such as an electrochemical cell, converts chemical energy into electrical energy. In a fuel cell, hydrogen, coming for example from any carbon-based fuel such as gas, a petroleum based oil product, or methanol, is combined with oxygen drawn from the air in order to produce electricity, water and heat by means of an electrochemical reaction. The core of the fuel cell is composed of an anode, a cathode and an electrolyte which is a solid ceramic-based electrolyte. The oxygen ions flow through the electrolyte and the electrical current flows from the cathode to the anode.
SOFCs (Solid Oxide Fuel Cells) are fuel cells that usually operate at high temperatures, of around 650 to 1000° C. They can be used in steady-state high-power (250 kW) and low-power (1 to 50 kW) supply systems. They are potentially advantageous owing to their high electrical efficiency (generally around 50 to 70%) and owing to the use of the heat that they produce.
Current SOFC materials operate at temperatures of about 900 to 1000° C. and will be explained below. The solid electrolyte most commonly used is yttrium-stabilized zirconia or YSZ. The anode, which is in particular the site of the reaction between H2 and the O2− anions coming from the electrolyte, is most commonly a cermet (a metal/ceramic composite) of the type in which nickel is dispersed in stabilized zirconia (YSZ), optionally doped with ruthenium Ru. The cathode, which collects the charges and is the site of the reduction of oxygen, which then diffuses in the O2− anion state through the electrolyte, is most usually based on an oxide of perovskite structure, such as lanthanum manganite doped with strontium (La,Sr)MnO3±δ. Finally, bipolar plates, or interconnectors, are present, generally there being two of them, and their function is to collect the charges at the anode and at the cathode and to separate the two gases, namely fuel (H2) and oxidizer (O2).
Now, the operation of the cell at such a high temperature poses many problems, especially the cost of the interconnectors and the chemical and above all mechanical behavior of the materials at temperature. This is why it has been envisaged to lower the operating temperature of the cell, to around 600-800° C. This would allow Inconel® (a heat-resistant alloy based on Ni, Cr and Fe) or stainless steels to be used as interconnectors. The electrolyte that has been envisaged for replacing YSZ is cerium oxide doped with gadolinium oxide, CeO2:Gd2O3(Ce0.9Gd0 1O1 95) with a fluorite structure, or a substituted LaGaO3 perovskite La0.9,Sr0.1Ga0.8Mg0 2O2 85). The anode could be based on vanadium chromite. As regards the cathode, various materials have been studied, including perovskites of the ABO3 type, and in particular doped LaMnO3 for reasons of good mechanical behavior, which may or may not be deficient on the A sites, and above all oxygen-deficient perovskites ABO3−δ such as (La,Sr)CoO3−δ. It remains the case that, at the present time, there is no material making it possible to use the cathode with, simultaneously, high electronic conductivity, a high ionic conductivity, good thermal stability and sufficient efficiency from the industrial standpoint.
It was to solve these problems of the prior art that another type of oxide material had to be sought. The material according to the invention does this,